Dielectric films having thin optically reflecting metallic coatings on the back side thereof have been used as the outer layer of multi layer thermal blankets employed for the temperature control of spacecraft. It is well known that spacecraft in earth orbit are subject to constant bombardment by charged particles of both positive and negative polarity. Therefore, such dielectric film surfaces can become charged to a very high potential in a space plasma environment. In certain circumstances, the resulting potentials due to this bombardment can be quite high, and break down field strengths can be exceeded. Furthermore, the energy associated with charge storage on a large area thin dielectric can be very large by the time normal breakdown potentials are reached.
It is known that in certain types of spacecraft, the induced potentials have caused different, electrically isolated segments of the spacecraft surface to assume greatly divergent potentials. This potential difference can become great enough to cause an electric discharge between the different segments, resulting in damage to electronic circuitry within the spacecraft.
U.S. Pat. No. 3,906,308 to Amason et al discloses the use of an aircraft lightning protection system utilizing dielectric materials in the form of coatings and/or films applied to critical components of the aircraft. The patent states that test data have been obtained using a Kapton film as a shielding material on an aluminum honeycone core composite test panel, as described in column 10 of the patent. In operation, the dielectric material is applied to a portion of the aircraft in which a component is to be protected. Current due to lightning is thus prevented from attaching to or transferring through the protected component due to the reduced conducting properties of the dielectric material. To protect large aircraft skin areas, metal strips of appropriate dimensions are affixed or bonded on the dielectric material surface to provide conduction paths for the lightning current. In contrast to the present invention, Amason et al does not appear to teach any puncturing of the outer dielectric film in order to make or facilitate the making of electrical conduction paths.
U.S. Pat. No. 3,989,984 to Amason et al and U.S. Pat. No. 3,755,713 to Paszkowski relate to aircraft lightning protection means and aircraft static electricity control means consisting of conductive mesh structures attached to the outer surface of a nonconductive material on the aircraft's outer surface. Again, the puncturing of the nonconductive material to facilitate electrical conduction is not disclosed or suggested by these references.
U.S. Pat. No. 3,184,742 to Cutler discloses a balloon communication satellite which utilizes a perforated structure as part of a method for obtaining desired heat transmission characteristics. However, Cutler describes the outer surface of the balloon communication satellite as consisting of a perforated aluminum coating 16 on a mylar sheet 14. Thus, the structural design is the reverse of that of the present invention. Further, it is noted that the Cutler disclosure is not directly concerned with reducing charge buildups on the outer surface of spacecraft.
U.S. Pat. No. 3,984,730 to Hunter relates to a method and apparatus for neutralizing potentials induced on spacecraft surfaces. However, in contrast to the present invention, the apparatus operates by generating charged particles which are released on the surface of the spacecraft to counteract charge buildups which have been sensed by charged particle detectors located on the surface of the spacecraft.
Examples of other devices which relate to subject matter similar to that of the present application include the following: U.S. Pat. No. 3,283,210 to Welsh; U.S. Pat. No. 3,968,405 to Testone; U.S. Pat. No. 3,971,024 to Clark, U.S. Pat. No. 2,583,540 to Bennett; U.S. Pat. No. 3,106,663 to Tanner; U.S. Pat. No. 3,170,087 to Tanner; and U.S. Pat. No. 3,633,068 to Miller.